Most present day alphanumeric displays have a fixed screen format or layout i.e. they have a fixed number of characters per row and a fixed number of rows. An example of this type of display is the IBM 3270 Information Display System manufactured by International Business Machines Corporation.
Display systems are also known which allow what is known as a split screen layout. In this layout, characters are displayed as a left hand section and a right hand section separated by a vertical blank column. Possible methods of performing this split screen layout are either to rearrange storage locations in a refresh buffer and use fixed addressing during refresh or to allow a controller to determine screen position of displayed data by microcode, and again use fixed addressing.
Both of these methods are unsuitable for the above mentioned Information Display System as the possible 32 CRT screens controlled by a single controller would have degraded performance due to the additional microcode and software execution.
In the prior art UK Pat. No. 1,178,749 proposes a display system in which different screen layouts are obtained by having a characteristic raster pattern for each screen layout.
Displays with split screen layout are used in the Newspaper Industry as it is easier when comparing an article with an edited version of the same article to have them displayed side by side. Also displays with special screen formats are required to display the Japanese language and Hanguel characters for the Korean national language.